Topcoats for use in immersion lithography

ABSTRACT

A method of forming a top coat layer and a topcoat material for use in immersion lithography. A topcoat layer is formed on a photoresist layer from an aqueous solution that is immiscible with the photoresist layer. The topcoat layer is then rendered insoluble in neutral water but remains soluble in aqueous-base developer solutions so the photoresist may be exposed in a immersion lithographic system using water as the immersion fluid, but is removed during photoresist development. The topcoat materials are suitable for use with positive, negative, dual tone and chemically amplified (CA) photoresist.

RELATED APPLICATIONS

This application is a division of co-pending application Ser. No.11/145,288.

FIELD OF THE INVENTION

The present invention relates to the field of integrated circuitfabrication; more specifically, it relates integrated circuitmanufacture utilizing immersion photolithography technology.

BACKGROUND OF THE INVENTION

Immersion lithography is rapidly emerging as an importantmicroelectronics fabrication technology. In immersion lithography aliquid is placed between the last optical element of the immersionlithography tool and photoresist layer. The optical properties of theliquid allow improved resolution and depth of focus to be attained. Onekey issue associated with immersion lithography is that the potentialexists for photoresist degradation and for contamination of the opticalcomponents through leaching of photoresist components into the liquidlayer. Topcoat materials applied over the resist layer are beingexamined as a means of suppressing this extraction.

Two types of topcoats currently exist. The first types of topcoats arewater-insoluble requiring a topcoat stripping process prior tophotoresist development. The second types of topcoats arewater-insoluble but aqueous-base soluble which are readily removedduring photoresist development but have the problem of tending todissolve the photoresist layer and leave interfacial layers where thephotoresist and topcoat layers were in contact.

Therefore, there is a continuing need for improved topcoat materials andmethods of forming topcoat layers.

SUMMARY OF THE INVENTION

A topcoat layer is formed on a photoresist layer from a solution that isimmiscible with the photoresist layer. The topcoat layer is thenrendered insoluble in neutral water but remains soluble in aqueous-basedeveloper solution so the photoresist may be exposed in a immersionlithographic system using water as the immersion fluid, but is removedduring photoresist development. The topcoat materials are suitable foruse with positive, negative, dual tone and chemically amplified (CA)photoresist.

A first aspect of the present invention is a topcoat composition,comprising: a polymer comprising monomers having the structure:

where R₁ is selected from the group consisting of a carboxylic acidgroup having 1 to 4 carbon atoms, R₂ is an alkyl ester group of the form—CO—O—R′ where R′ is an alkyl group having 1 to 4 carbon atoms, and R₃and R₄ are each independently selected from the group consisting ofhydrogen, a linear alkyl group having 1-6 carbon atoms, a branched alkylgroup having 2-12 carbon atoms, an alicyclic group having 3-8 carbonatoms, an alkyl ester group having 2 to 5 carbon atoms, an alkyl ethergroup having 2 to 8 carbon atoms, and a fluorinated alcohol group 1-12carbon atoms; a volatile base; and water.

A second aspect of the present invention is a topcoat composition,comprising: a polymer comprising: a first monomer having the structure:

and a second monomer having the structure:

where R₁ is selected from the group consisting of a carboxylic acidgroup having 1 to 4 carbon atoms, R₂ is an alkyl ester group of the form—CO—O—R′ where R′ is an alkyl group having 1 to 4 carbon atoms, and R₃,R₄, R₅, R₆, R₇ and R₈ are each independently selected from the groupconsisting of hydrogen, a linear alkyl group having 1-6 carbon atoms, abranched alkyl group having 2-12 carbon atoms, an alicyclic group having3-8 carbon atoms, an alkyl ester group having 2 to 5 carbon atoms, analkyl ether group having 2 to 8 carbon atoms, and a fluorinated alcoholgroup having 1-12 carbon atoms; a volatile base; and water.

A third aspect of the present invention is a topcoat composition,comprising: a polymer selected from the group consisting ofpoly(isobornyl methacrylate-co-methyl methacrylate-co-tert-butylmethacrylate-co-methacrylic acid) copolymer, poly(methylmethacrylate-co-methacrylic acid) copolymer and combinations thereof;ammonia; and water.

BRIEF DESCRIPTION OF DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of an illustrative embodiment when readin conjunction with the accompanying drawings, wherein:

FIG. 1A is an infrared spectrum of a topcoat layer prepared according toan embodiment of the present invention and FIG. 1B is an infraredspectrum of a topcoat layer prepared by a control method;

FIG. 2A is a top view and FIG. 2B is a sectional view of the line-spacearray that results after post-expose bake and development of aphotoresist layer in aqueous-base developer of a control sample of afirst experiment;

FIG. 3A is a top view and FIG. 3B is a sectional view of the line-spacearray that results after post-expose bake and development of aphotoresist layer in aqueous-base developer of an experimental sample ofthe first experiment;

FIG. 4A is a sectional view of the line-space array that results afterpost-expose bake and development of a photoresist layer in aqueous-basedeveloper of a first control sample of a second experiment;

FIG. 4B is a sectional view of the line-space array that results afterpost-expose bake, removal of a topcoat layer, and development of aphotoresist layer in aqueous-base developer of a second control sample;

FIG. 4C is a sectional view of the line-space array that results afterpost-expose bake and development of a photoresist layer in aqueous-basedeveloper of an experimental sample of the second experiment;

FIGS. 5A through 5C are partial cross-sectional views illustrating asemiconductor manufacturing process step according to an embodiment ofthe present invention; and

FIG. 6 is a diagram of an exemplary immersion photolithographic systemthat may be used to process a semiconductor wafer having a topcoat layeraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Topcoat layers according to embodiments of the present invention mayadvantageously have the following solubility properties: (1) the topcoatlayer does not dissolve or swell the underlying photoresist layer duringapplication; (2) the topcoat layer is insoluble in neutral water duringimmersion exposure; and (3) the topcoat layer is soluble in aqueous-baseduring development. Neutral water is defined as water having a pH ofbetween 6 and about 8. Topcoat layers according to the embodiments ofthe present invention are applied from an aqueous-base solution aspolymers having pendent ionic groups. The topcoat layers may be applied,for example, by spin-coating. During evaporation of water duringspinning and/or during an optional post-apply heating step (post bake),the pendent ionic groups undergo conversion to a neutral form. Theneutral form renders the polymers insoluble in water. However, theneutral form retains its intrinsic solubility in aqueous-base so duringphotoresist development in aqueous-base developers the topcoat layer isremoved without the need for a separate topcoat stripping step prior tophotoresist development.

Topcoat layers of embodiments of the present invention may compriseacrylic polymers or copolymers having exemplary structures (I) or (II):

where R₁ is selected from the group consisting of a carboxylic acidgroup having 1 to 4 carbons, R₂ is an alkyl ester group of the form—CO—O—R′ where R′ is an alkyl group having 1 to 4 carbon atoms and R₃,R₄, R₅, R₆, R₇ and R₈ are each independently selected from the groupconsisting of hydrogen, a linear alkyl group having 1-6 carbon atoms, abranched alkyl group having 2-12 carbon atoms, an alicyclic group having3-8 carbon atoms, an alkyl ester group having 2 to 5 carbon atoms, analkyl ether group having 2 to 8 carbon atoms, and a fluorinated alcoholgroup having 1-12 carbon atoms.

The R₁ pendent group is an acid group selected to ionize (disassociatefrom its acidic —H group, thereby increasing its polarity) in a basicaqueous solution (a solution having a pH greater than about 11) andrevert to its neutral (less polar, associated, un-ionized) acid formupon removal of the base from solution. For example, if the pendentgroup is —COOH in its neutral state, in the presence of NH₃ the pendentgroup would react with NH₃ in aqueous solution to form —COO⁻ and NH₄ ⁺ions rendering the polymer soluble. Heat would drive off the NH₃ andreconstitute the —COOH pendent group, rendering the polymer insoluble inneutral or acidic aqueous solutions. The R₁ pendent group should besubstantially transparent to the actinic radiation used by the immersionlithography system to expose the photoresist layer. The R₁ pendent groupshould not react with the photoresist layer in a manner to adverselyaffect the imaging quality of the photoresist layer.

The R₂, R₃, R₄, R₅, R₆, R₇ and R₈ pendent groups that are not H shouldcause the polymer/copolymer to be insoluble in water when the R₁ pendentgroup is not ionized. The R₂, R₃, R₄, R₅, R₆, R₇ and R₈ pendent groupsshould be substantially transparent to the actinic radiation used by theimmersion lithography system to expose the photoresist layer. The R₂,R₃, R₄, R₅, R₆, R₇ and R₈ pendent groups should not react with thephotoresist layer in a manner to adversely affect the imaging quality ofthe photoresist layer. The R₂, R₃, R₄, R₅, R₆, R₇ and R₈ pendent groupsshould not react with the R₁ pendent group.

Topcoat solutions according to this embodiment of present invention maycomprise water solutions of polymer (I) or polymer (II) and a volatilebase such as NH₃, CH₃NH₂, (CH₃)₂NH, (CH₃)₃N, CH₃CH₂NH₂, (CH₃CH₂)₂NH,(CH₃CH₂)₃N, other amines and combinations thereof.

The topcoat is formed by applying the topcoat solution to a photoresistlayer to form a precursor layer, heating the precursor layer to driveoff any residual water and the volatile base and convert the polymer (I)or polymer (II) to its non-water soluble but aqueous-base soluble form.

EXPERIMENTAL First Preparation

A 4% by weight aqueous solution of the ionic form of the copolymerpoly(isobornyl methacrylate-co-methyl methacrylate-co-tert-butylmethacrylate-co-methacrylic acid) (IBM-MMA-TBMA-MAA), 25:30:10:35 mole %ratio (hereinafter polymer III) was prepared by combining 480 mg of thecarboxylic acid form of polymer III, 12 ml of water and 9/20 ml ofconcentrated (29% by weight) ammonium hydroxide.

As the following reactions show, the carboxylic acid form of polymer III(which is insoluble in neutral water) reacts with NH₄OH in H₂O to formthe ionized and water soluble form of polymer III. The ionized form ofpolymer III may be converted back to the carboxylic acid form by heatingthe ionized form of polymer III to drive off NH₃.

In the absence of ammonium hydroxide, the carboxylic acid form ofpolymer III is insoluble in neutral water, but by adding ammoniumhydroxide the polymer is solubilized by ionization of the carboxylicacid groups, to yield a clear, colorless solution.

1/20 ml of the 4% by weight aqueous solution of the ionic form ofIBM-MMA-TBMA-MAA was applied on a silicon wafer, and the resulting layerwas heated at 110° C. for 90 seconds. An infrared spectrum of theresulting layer was recorded and is shown in FIG. 1A. For comparisonpurposes FIG. 1B is an infrared spectrum of a layer of the carboxylicacid form of IBM-MMA-TBMA-MAA made by dissolving the carboxylic acidform of IBM-MMA-TBMA-MAA in propylene glycol methyl ether acetatesolvent, spin-applied to a silicon wafer, and baked at 110° C. for 90seconds. The infrared spectra of FIGS. 1A and 1B are a very close match,indicating the starting material has been reconstituted. The presence ofsubstantial amounts of carboxylate ion would be indicated in FIG. 1A bythe presence of an absorption band in the 1610-1550 cm⁻¹ region which isnot present.

Two experiments using polymer III based topcoat material were conducted.

For a control sample in the first experiment, an antireflection layer ofAR3-600 manufactured by Rohm and Haas Electronic Materials, Marlborough,Mass. was formed on a first silicon wafer. A 100 nm thick layer of TOKILPEM01, a CA photoresist manufactured by Tokyo Ohka Kogyo, Kanagawa,Japan and designed for immersion lithography, was formed on top of theantireflection layer. After baking the photoresist layer, the wafer wasexposed using a liquid immersion interferometric lithography systemoperating at a wavelength of 257 nm to form a series of line-spacearrays of 180 nm pitch. Water was used as the immersion fluid. FIG. 2Ais a top view and FIG. 2B is a sectional view of the line-space arraythat results after post-expose bake and development of the photoresistlayer in aqueous-base developer of the control sample, both taken byscanning electron microscopy (SEM).

For an experimental sample in the first experiment, an antireflectionlayer of AR3-600 was formed on a second silicon wafer. A 100 nm thicklayer of TOK ILPEM01 photoresist, was formed on top of theantireflection layer. After post-apply baking the photoresist layer butprior to exposure, a precursor topcoat layer was formed using theaqueous solution of the ionized form of polymer III described supra, ontop of the photoresist layer. After application of the topcoat layer,the wafer was subjected to a topcoat post-apply bake at 110° C. for 90seconds. After baking the wafer, the wafer was exposed using a liquidimmersion interferometric lithography system operating at a wavelengthof 257 nm to form a series of line-space arrays of 180 nm pitch. Waterwas used as the immersion fluid. FIG. 3A is a top view and FIG. 3B is asectional view of the line-space array that results after post-exposebake and development of the photoresist layer in aqueous-base developerof the experimental sample, both taken by SEM.

By comparing FIG. 2A with FIG. 3A and FIG. 2B with FIG. 3B, it can beseen that images formed with a topcoat of an embodiment according to thepresent invention are comparable in quality to those formed without atopcoat, and the photoresist photosensitivity is essentially unchanged.Both these characteristics indicate that application of the topcoatsolution has not caused significant base contamination of the underlyingphotoresist layer. It should be understood that CA resists are extremelysensitive to base contamination, especially ammonia and amine basedbases.

For a first control sample in the second experiment, an antireflectionlayer of AR3-600 was formed on a first silicon wafer. A 150 nm thicklayer of TOK P6111, a CA photoresist manufactured by Tokyo Ohka Kogyo,Kanagawa, Japan and useful for immersion lithography, was formed on topof the antireflection layer. No topcoat was applied. After post-applybaking of the photoresist layer, the wafer was exposed in air (not underliquid immersion) using an interferometric lithography system operatingat 257 nm wavelength to image a series of line-space arrays with 180 nmpitch. FIG. 4A is a sectional view of the line-space array that resultsafter post-expose bake and development of the photoresist layer inaqueous-base developer of the first control sample taken by SEM. Thewebbing between adjacent lines is a consequence of airborne basiccontamination present in the process environment.

For a second control sample in the second experiment, an antireflectionlayer of AR3-600 was formed on a second silicon wafer. A 150 nm thicklayer of TOK P6111 photoresist was formed on top of the antireflectionlayer. After post-apply baking of the photoresist layer, a layer of TOKTSP-3A fluoropolymer topcoat manufactured by Tokyo Ohka Kogyo, Kanagawa,Japan was applied on top of the antireflective layer and post-applybaked at 90° C. for 60 seconds. The wafer was exposed in air (not underliquid immersion) using an interferometric lithography system operatingat 257 nm wavelength to form a series of line-space arrays with 180 nmpitch. FIG. 4B is a sectional view of the line-space array that resultsafter post-expose bake, removal of the topcoat layer with a proprietaryorganic solvent stripper, and development of the photoresist layer withaqueous-base developer of the second control sample taken by SEM. Thewebbing that was present in FIG. 4A is absent, a consequence of theprotective benefit of the topcoat layer against airborne basiccontamination present in the environment.

For a experimental sample in the second experiment, an antireflectionlayer of AR3-600 was formed on a third silicon wafer. A 150 nm thicklayer of TOK P6111 photoresist was formed the antireflection layer.After post-apply baking the photoresist layer but prior to exposure, atopcoat layer was formed using the aqueous solution of the ionized formof polymer III described supra, on top of the photoresist layer. Afterapplication of the topcoat layer, the wafer was subjected to a topcoatpost-apply bake at 110° C. for 90 seconds. The wafer was exposed inliquid immersion mode using a liquid immersion interferometriclithography system operating at 257 nm wavelength to form a series ofline-space arrays with 180 nm pitch. FIG. 4C is a sectional view of theline-space array that results after post-expose bake and development ofa photoresist layer in aqueous-base developer of an experimental sampleof the second experiment. The photoresist images of FIG. 4C areessentially identical to those of FIG. 4B. This serves to demonstratethat the carboxylic acid form of polymer III topcoat layer functions asa barrier layer and that application of the ionized form of polymer IIIcontaining NH₃ does not cause significant base contamination of theunderlying photoresist layer nor is there any indication for theformation of an interfacial layer between topcoat and photoresist.

These two experiments have produced unexpected results because of theknown sensitivity of CA photoresists to ammonia and organic amines, bothBronsted bases. A Bronsted base is a molecule that can accept a proton.A Bronsted acid is a molecule that can donate a proton. In a CAphotoresist, a small quantity of a Bronsted acid is formed upon exposureof the photoresist layer to actinic radiation. In a subsequent thermalstep this acid acts to catalyze a chemical reaction (typically anacidolysis or a cross-linking) to cause a large change in the solubilityof the polymer in the exposed regions of the photoresist layer. The neteffect of the acid catalysis is a large gain in the photosensitivity ofthe resist, but one drawback is that CA resists are sensitive to tracequantities of ammonia or amines (airborne bases) which disrupt theacid-catalyzed step by acid-base neutralization. Exposing a CAphotoresist in air containing as little as 15 ppb is enough to renderany photoresist patterns obtained useless.

Second Preparation

A 4 wt % solution of the ionic form of the copolymer poly(methylmethacrylate-co-methacrylic acid) (PMMA-MAA), 20 moel % methacrylic acidby NMR analysis, molecular weight 12800, polydispersity 1.83;(hereinafter polymer IV) was prepared by combining 160 mg of thepolymer, 4 ml of water and 3/20 ml of concentrated (29%) ammoniumhydroxide solution.

As the following reactions show, the carboxylic acid form of polymer IV(which is insoluble in neutral water) reacts with NH₄OH in H₂O to formthe ionized and water soluble form of polymer IV. The ionized form ofpolymer IV may be converted to the carboxylic acid form by heating todrive off NH₃.

In the absence of the added ammonium hydroxide, the carboxylic acid formof polymer IV is insoluble in neutral water, but by adding ammoniumhydroxide the polymer is solubilized by ionization of the carboxylicacid groups, to yield a clear, colorless solution.

A topcoat layer can be prepared from an aqueous solution of the ionicform of polymer IV by spin-coating, followed by a post-apply bake at110° C. for 90 seconds. The resulting topcoat layer comprises thecarboxylic acid form of polymer IV and is insoluble in neutral water butrapidly dissolves in 0.26 N tetramethyl ammonium hydroxide developer.

For a control sample, a deep ultraviolet antireflection layer was formedon a first silicon wafer. A 190 nm thick layer of JSR AR1682J, a CAphotoresist manufactured by JSR Micro, Sunnyvale California was formedon top of the antireflection layer. After baking the photoresist layer,the wafer was exposed by contact printing with broad-band 254 nm lightusing a step-wedge pattern mask to obtain a range of exposure dosesbetween 7 and 18 mJ/cm² at the wafer plane. The photoresist layer wasthen post-expose-baked at 110° C. for 90 seconds to activate the resistimaging chemistry and developed for 30 seconds in CD-26 developer (abasic developer) manufactured by Rohm and Haas Electronic Materials,Marlborough, Mass.

For an experimental sample, a second silicon wafer was prepared andtreated identically to the first silicon wafer with the exception that alayer of the ionic form of polymer IV was spin-coated and then baked at110° C. for 90 seconds to drive out the ammonia and generate a layer ofthe carboxylic acid form of polymer IV on top of the photoresist layer.After baking the photoresist layer, the wafer was exposed by contactprinting with broad-band 254 nm light using a step-wedge pattern mask toobtain a range of exposure doses between 7 and 18 mJ/cm² at the waferplane. The photoresist layer was then post-expose-baked at 110° C. for90 seconds to activate the resist imaging chemistry and developed inCD-26 developer for 30 seconds.

Both wafers showed well defined and fully developed relief patterns atthe highest dose and partial development of patterns at lower doses.There was no significant difference in photoresist sensitivity betweenthe two wafers apparent from this experiment.

FIGS. 5A through 5C are partial cross-sectional views illustrating asemiconductor manufacturing process according to a embodiment of thepresent invention. In FIG. 5A, a substrate 30 is provided. In oneexample, substrate 30 is a semiconductor substrate. Examples ofsemiconductor substrates include but are not limited to bulk (singlecrystal) silicon wafers and silicon on insulator (SOI) wafers. Formed ona top surface 35 of substrate 30 is an optional antireflective coating(ARC) 40. In one example, ARC 40 is spin applied and a post ARC applybake (heated above room temperature to remove most of the ARC solvent)performed. Formed on a top surface 45 of ARC 40 is a photoresist layer50. In one example, photoresist layer 50 is spin applied and a postphotoresist apply bake, also known as a pre-exposure bake or a pre-bake(heated above room temperature to remove most of the photoresistsolvent) is performed. Next a topcoat 60 is formed on a top surface 55of photoresist layer 50. Topcoat 60 comprises a carboxylic acid form ofa polymer or copolymer as described supra. Topcoat 60 is spin appliedfrom an aqueous solution containing a volatile base such as ammonia oran organic amine and a post topcoat apply bake (heated above roomtemperature to remove the water and drive out the volatile base) isperformed and forms a topcoat layer that is not miscible withphotoresist layer 50 or soluble in neutral water.

In FIG. 5B, a layer of immersion fluid 70 is formed over a top surface75 of topcoat 60 in an immersion photolithography tool (see FIG. 6 anddescription infra). An example of an immersion fluid is water, with orwithout additives. Light of a wavelength to which photoresist layer 50is sensitive is passed through a photomask 80. Photo mask 80 has clearregions 85 that transmit the light and opaque regions 90 that block thelight. Exposure of photoresist layer 50 to light through mask 80 formsunexposed regions 95A of photoresist layer 50 and exposed regions 95B ofphotoresist layer 50. Exposed regions 95B are also known as latent imageregions. An optional post exposure bake (heated above room temperatureto drive the photoresist chemistry) may be performed.

Although a positive photoresist is shown in FIG. 5B, the embodiments ofthe present invention also work well with negative photoresist systemsor dual tone photoresist systems. The embodiments of the presentinvention are well suited for use with chemically amplified resists. Innegative photoresist systems, the photoresist will develop away where itis not exposed to light, so a photomask of polarity opposite to thatillustrated in FIG. 5B is required. Dual tone resists can act eithernegatively or positively depending upon the developer system used.

In FIG. 5C, substrate 30 is removed from the immersion photolithographytool and photoresist layer 50 developed to remove exposed regions 95B(see FIG. 5B) and leave behind unexposed regions 95A. In one example thedeveloper comprises an aqueous solution of a base such as tetramethylammonium hydroxide (TMAH). Topcoat 60 (see FIG. 5B) is also removed bythe developer. An optional post development bake, (heated above roomtemperature to harden the photoresist images) may be performed.

While the exposure of the photoresist layer was described in the contextof an immersion photolithography system, the topcoat compositionsaccording to embodiments of the present invention also have utility in aconventional (non-immersion) photolithography system as illustrated bythe comparison of FIGS. 6A and 6B described supra. The topcoatsaccording to embodiments of the present invention may act as protectivecoatings against environmental contamination from volatile bases such asammonia and organic amines that could degrade the imaging process orcause imperfections in the photoresist images and ultimately yieldreliability defects in the fabricated product when the photoresist is aCA photoresist.

FIG. 6 is a diagram of an exemplary immersion photolithographic systemthat may be used to process a semiconductor wafer having a topcoat layeraccording to the present invention. In FIG. 6 an immersion lithographysystem 100 includes a controlled environment chamber 105 and acontroller 110. Contained within controlled environment chamber 105 is afocusing mirror 115, a light source 120, a first focusing lens (or setof lenses) 125, a mask 130, an exposure slit 135, a second focusing lens(or set of lenses) 140, a final focusing lens 145, an immersion head 150and a wafer chuck 155. Immersion head 150 includes a transparent window160, a central chamber portion 165, a surrounding plate portion 170, animmersion fluid inlet 175A and an immersion fluid outlet 175B. Animmersion fluid 180 fills central chamber portion 165 and contacts a topsurface 185 of topcoat layer 60 formed on a top surface of photoresistlayer 50 formed on a top surface of substrate 30. Topcoat layer 60comprises a carboxylic acid form of a polymer or copolymer as describedsupra. Alternatively, an optional ARC layer may be formed betweensubstrate 30 and photoresist layer 50. In one example, immersion fluid180 includes water. Plate portion 170 is positioned close enough totopcoat layer 60 to form a meniscus 190 under plate portion 170. Window160 must be transparent to the wavelength of light selected to exposephotoresist layer 50.

Focusing mirror 115, light source 120, first focusing lens 125, a mask130, exposure slit 135, second focusing lens 140, final focusing lens145, immersion head 150 are all aligned along an optical axis 200 whichalso defines a Z direction. An X direction is defined as a directionorthogonal to the Z direction and in the plane of the drawing. A Ydirection is defined as a direction orthogonal to both the X and Zdirections. Wafer chuck 155 may be moved in the X and Y directions underthe direction of controller 110 to allow formation of regions of exposedand unexposed photoresist in photoresist layer 50. As wafer chuck 155moves, new portions of photoresist layer 50 are brought into contactwith immersion fluid 180 and previously immersed portions of thephotoresist layer are removed from contact with the immersion fluid.Mask 130 and slit 135 may be moved in the Y direction under the controlof controller 110 to scan the image (not shown) on mask 130 ontophotoresist layer 50. In one example, the image on mask 130 is a 1× to a10× magnification version of the image to be printed and includes one ormultiple integrated circuit chip images.

When exposure is complete, substrate 30 is removed from controlledenvironment chamber 105 without spilling immersion fluid 185. To thisend, controlled environment chamber 105 also includes a cover plate 205that may be moved to first abut with wafer chuck 155 and then moved withthe wafer chuck as the wafer chuck is moved out of position from underimmersion head 150, the cover plate replacing the wafer chuck underimmersion head 150.

The topcoat compositions according to embodiments of the presentinvention may be used with other types of immersion lithography tools,an example of which is an immersion lithography tool wherein theimmersion fluid is dispensed onto the wafer from openings in the lensbarrel surrounding the lens.

Thus the embodiments of the present invention provide improved topcoatmaterials and methods of forming topcoat layers to wit, the topcoatlayers according to embodiments of the present invention have theadvantages that they can be formed from aqueous solution thus avoidinglayer intermixing with the photoresist layer, are insoluble in waterduring immersion exposure thus remaining intact and of constantthickness throughout the entire photoresist exposure process, and arecompletely removed during the photoresist development step thus avoidingthe need for a separate pre-photoresist develop topcoat removal step.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

1. A topcoat composition, comprising: a polymer comprising monomershaving the structure:

where R₁ is selected from the group consisting of a carboxylic acidgroup having 1 to 4 carbon atoms, R₂ is an alkyl ester group of the form—CO—O—R′ where R′ is an alkyl group having 1 to 4 carbon atoms, and R₃and R₄ are each independently selected from the group consisting ofhydrogen, a linear alkyl group having 1-6 carbon atoms, a branched alkylgroup having 2-12 carbon atoms, an alicyclic group having 3-8 carbonatoms, an allcyl ester group having 2 to 5 carbon atoms, an alkyl ethergroup having 2 to 8 carbon atoms, and a fluorinated alcohol group 1-12carbon atoms; a volatile base; and water.
 2. The composition of claim 1,wherein said volatile base is a material selected from the groupconsisting of NH₃, CH₃NH₂, (CH₃)₂NH, (CH₃)₃N, CH₃CH₂NH₂, (CH₃CH₂)₂NH,(CH₃CH₂)₃N, other amines and combinations thereof.
 3. The composition ofclaim 1, wherein said volatile base is NH₃.
 4. The composition of claim3, wherein about 3.6% by volume of said composition consists ofconcentrated aqueous NH₄OH.
 5. The composition of claim 1, wherein about4% by weight of said compositions consists of said polymer.
 6. Thecomposition of claim 1, wherein said R₂, R₃ and R₄ groups are notcapable of reacting with said R₁ group.
 7. The composition of claim 1,wherein said R₂, R₃ and R₄ groups that are not H cause said polymer tobe insoluble in water when said R₁ group is not ionized.
 8. A topcoatcomposition, comprising: a polymer comprising: a first monomer havingthe structure:

 a second monomer having the structure:

where R₁ is selected from the group consisting of a carboxylic acidgroup having 1 to 4 carbon atoms, R₂ is an alkyl ester group of the form—CO—O—R′ where R′ is an alkyl group having 1 to 4 carbon atoms, and R₃,R₄, R₅, R₆, R₇ and R₈ are each independently selected from the groupconsisting of hydrogen, a linear alkyl group having 1-6 carbon atoms, abranched alkyl group having 2-12 carbon atoms, an alicyclic group having3-8 carbon atoms, an alkyl ester group having 2 to 5 carbon atoms, analkyl ether group having 2 to 8 carbon atoms, and a fluorinated alcoholgroup having 1-12 carbon atoms; a volatile base; and water.
 9. Thecomposition of claim 8, wherein said volatile base is a materialselected from the group consisting of NH₃, CH₃NH₂, (CH₃)₂NH, (CH₃)₃N,CH₃CH₂NH₂, (CH₃CH₂)₂NH, (CH₃CH₂)₃N, other amines and combinationsthereof.
 10. The composition of claim 8, wherein said volatile base isNH₃.
 11. The composition of claim 10, wherein about 3.6% by volume ofsaid composition consists of concentrated aqueous NH₄OH.
 12. Thecomposition of claim 8, wherein about 4% by weight of said compositionsconsists of said polymer.
 13. The composition of claim 8, wherein saidR₂, R₃, R₄, R₅, R₆, R₇ and R₈ groups are not capable of reacting withsaid R₁ group.
 14. The composition of claim 8, wherein said R₂, R₃, R₄,R₅, R₆, R₇ and R₈ groups that are not H cause said polymer to beinsoluble in water when said R₁ group is not ionized.
 15. A topcoatcomposition, comprising: a polymer selected from the group consisting ofpoly(isobornyl methacrylate-co-methyl methacrylate-co-tert-butylmethacrylate-co-methacrylic acid) copolymer, poly(methylmethacrylate-co-methacrylic acid) copolymer and combinations thereof;ammonia; and water.
 16. The topcoat composition of claim 15, whereinsaid polymer consists of poly(isobornyl methacrylate-co-methylmethacrylate-co-tert-butyl methacrylate-co-methacrylic acid) copolymer.17. The topcoat composition of claim 15, wherein said polymer consistsof poly(methyl methacrylate-co-methacrylic acid) copolymer.
 18. Thetopcoat composition of claim 15, wherein about 3.6% by volume of saidtopcoat composition consists of concentrated aqueous NH₄OH.
 19. Thetopcoat composition of claim 15, wherein about 4% by weight of saidtopcoat composition consists of said polymer.